This invention relates to the field of spark gap technology and specifically to devices that are required to pass very high currents with very high rates of current increase. The invention pertains to an improved device of the character described in which the useful life of the electrodes is greatly increased or the value of ampere-second pulses passed by the switch is greatly increased for a given life.
The switch of the present invention has particular utility in systems that require repetitive current pulses of at least 100,000 A of at least 1 microsec duration, from source voltages of at least 1000 volts. In the present state of the art, a pair of electrodes is limited to a life of about 100,000 discharges when passing current pulses of about 10 microsecs duration and about 100,000 A amplitude. The invention permits significant extension of these values of electrode life or current amplitude or pulse duration or a combination of these parameters.
The utility of spark gap devices is limited by erosion of the electrode surfaces which reduces the life, or number of discharges after which the device becomes inoperative. The rate of erosion increases rapidly as the amplitude of switch current increases.
Erosion and deterioration of electrode surfaces is caused by very localized heating, vaporization, ion bombardment and electromagnetic forces. As this deterioration continues the geometry of the electrodes changes until the switch fails to function under the intended initial operating conditions.
In the past art, electromagnetic sweeping of the arc has been employed to reduce localized erosion. However, in all prior use of this technique the sweeping commences at zero velocity at the instant the arc is formed and increases with time as the electromagnetic force acts on the mass of the plasma. Hence, if the amplitude of the current is large at the start of the current pulse, localized erosion is not reduced at this instant and at the location of the start of the arc.